I get this error after a failed uninstall of a SQL instance of WinCC 2008 .

I list the properties of the Service SQL VSS and get "SQLWriter"

then, in the command prompt I type:

SC DELETE SQLWriter

Success, then I go to Control Panel -> Add/Remove Programs and Give to SQL SERVER VSS a "repair option", then i Choose the SQLWriter.msi file from instal files and ready! Problem Solved!